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TOUCHSCREEN
TECHNOLOGY
When
it comes to touchscreen technology, the most prevalent types
are Capacitive, Infrared, Resistive, SAW (surface acoustical
wave), Near Field Imaging and Guided Wave. The most widely
used touchscreens for industrial applications are Resistive
and Capacitive. All of these technologies have their own distinct
characteristics, both
advantageous and with limitations.
Capacitive
Touchscreens
Capacitive
touch screen technology is recommended for use in KIOSK applications
that require a "finger touch." It will not operate
with either a gloved hand or with a mechanical stylus. It
is made of glass, which makes it extremely durable and scratch
resistant. This glass overlay has a coating that stores the
charge deposited over its surface electrically. Capacitive
touchscreens operate using oscillator circuits that are located
in each corner of the glass overlay and measure the capacitance
of the area to be "touched." Depending on where
the person touches the overlay, the oscillators will vary
in frequency. Then a touchscreen controller measures the frequency
variations to ascertain the coordinates of the person's touch.
When used with flat panel displays, capacitive offers drift-free
stable performance that is not susceptible to deterioration
over time. A capacitive touchscreen is impervious to grease,
dirt and water, which makes it ideal for frequent use. It
can also be gasket sealed for NEMA 4 and NEMA 4x operation.
Since a capacitive touchscreen is made of glass, it is susceptible
to breakage.
Infrared
Touchscreens
Infrared
touch screen technology is based on "legacy" technology
and is becoming increasingly replaced by Resistive or Capacitive
touch systems. Over the years, Infrared bezels have proven
to be a very reliable technology for use in ATMs, Food Service
and Preparation, KIOSK, Medical Instrumentation, Process Control
Systems and Transportation Tracking applications. It does
not incorporate any sort of "overlay" that could
inhibit screen clarity or brightness, but instead uses a special
bezel of LEDs (light emitting diodes) along with diametrically
opposing phototransistor detectors which surround the glass
of the display surface. The controller circuitry scans the
screen with an invisible lattice of infra-red light beams
just in front of the surface that directs a sequence of pulses
to the LEDs. It then detects information at the location where
the LEDs have become interrupted by a stylus or finger. The
infrared frame housing the transmitters can impose design
constraints on operator interface products. A few limitations
are (1) that they usually require low resolution output of
the monitor, (2) can produce activation without touching the
screen and (3) the cost to produce the special Infrared bezel
is quite high.
Resistive
Touchscreens
Resistive
touch screen technology is recommended for use in POS (Point
of Sale): Grocery Stores, Hotels, Restaurants and Retail Stores;
Industrial Applications: MMI (Man Machine Interface), Machine
and Process Control; Portable Devices; Personal Information
Management Systems; Transportation Solutions; Medical Solutions:
Equipment, Instrumentation and Patient Monitoring Systems.
It generally uses a display overlay composed of layers, each
with a conductive coating on the interior surface. Special
separator "dots" are distributed evenly across the
active area and separate the conductive interior layers. The
pressure from using either a mechanical stylus or finger produces
an internal electrical contact at the "action point"
which supplies the controller with vertical and horizontal
analog voltages for data input. To reduce parallax for older
"curved" CRT applications only, resistive touchscreens
are generally spherical to match the curvature of the CRT
(true flat resistive touch overlays are also available for
TFT flat panels and/or CRTs). Our resistive touchscreens are
anti-glare to reduce reflective shine intensity, which will
slightly diffuse the light output throughout the screen. Resistive
technology offers tremendous versatility in that activation
can be initiated by: a gloved hand, fingernail, mechanical
stylus or an ungloved finger. Resistive touch screens can
be gasket sealed for NEMA 4 and NEMA 4X environments. Limitations
include: Low light output, diffused resolution images and
a plastic surface which can be scratched if improperly touched.
SAW
(Surface Acoustic Wave) Touchscreens
SAW touchscreen
technology is suggested for use in ATMs, Amusement Parks,
Banking and Financial Applications, Gaming Environments, Industrial
Control Rooms and KIOSK. SAW touch cannot be used within NEMA
environments, as the technology cannot be gasket sealed. It
has excellent durability that allows it to continue working
if scratched since the overlay for the touch sensor is a solid
glass display. The disadvantage to this glass overlay is that
it is breakable and won't work in washdown conditions. The
waves are spread across the screen by bouncing off reflector
arrays along the edges of the overlay. The waves are detected
by two "receivers." The acoustic wave weakens when
the user touches the glass with their finger, gloved hand
or soft stylus. The coordinates are then determined by the
controller circuitry that measure the time at which the amplitude
declines. It is the only technology that can produce a Z-coordinate
axis response. SAW offers superior image clarity, resolution
and high light transmission.
Near
Field Imaging Touchscreens
Near Field
Imaging touch screens are the preferred touch solution for
applications that require extreme durability in harsh environments.
NFI projected capacitive technology is accurate enough to
control equipment precisely, yet sensitive enough to detect
finger touches through gloves. Ideally suited for harsh environments,
NFI touch screens withstand high pressure washdowns common
in industrial or automotive manufacturing and are unaffected
by most surface contaminants found in factory automation,
utilities and mining environments. Near Field Imaging touch
technology is exceptional in its ability to detect touches
made by conductive objects- fingers or a conductive stylus
as well as through gloves and other potential barriers (moisture,
oil, gels and paints). Sophisticated sensing circuitry generates
a precise profile of a touch through highly specialized data
acquisition and image processing techniques. Made of strengthened
glass and a laminated construction with no mechanically sensitive
components, Near Field Imaging can withstand significant vibration
and shock in extreme environments.
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